1. Field of the Invention
The present invention relates to an endoscope apparatus in which an image pickup means and an image processing means are connected to each other by image transmitting means and, more particularly, to an endoscope apparatus in which an image pickup signal at a signal transmitting means is corrected for a delay time error.
2. Description of the Related Art
Conventionally, in an image pickup device of a so-called separation type in which a camera head section serving as image pickup means and a camera control unit serving as image processing means are separated from each other has the following disadvantage. That is, if length of a camera cable for transmitting an image pickup signal from a camera head is changed or altered, an error is generated in the propagation delay time of the image pickup signal. Thus, a circuit must be regulated such that the propagation delay time error is corrected each time the error is generated. For this reason, not only the operation of the image pickup device is complicated, but it is also impossible to perform regulation of the propagation delay time error with high accuracy. Particularly, in a case where signal processing such as optical black clamp is accurately performed with respect to the image signal as is in a high-grade television, the aforesaid disadvantage becomes or creates a large problem.
In order to solve the above-discussed disadvantage, Japanese Patent Laid-Open No. SHO 62-82782 (82782/1987) discloses a television camera apparatus in which a third cable is added which transmits a control signal to the outside of a cable for transmitting an image signal read out from a CCD and a cable for transmitting a drive signal of the CCD, a drive pulse is transmitted which is used to read out the CCD to a video processor section from a camera section through the third cable, and the drive pulse is utilized to sample the image signal read out from the CCD.
Further, Japanese Patent Laid-Open No. SHO 61-187470 (187470/1986) discloses a television camera apparatus in which a reset pulse contained or included in a CCD output signal supplied to a video processor section from a camera section is extracted, a sampling pulse synchronized with a phase of the reset pulse is created by a phase locked oscillator, and the CCD output signal is held in sample by the sampling pulse to take out or fetch the image signal.
However, the television camera apparatus disclosed in the aforesaid Japanese Patent Laid-Open No. SHO 62-82782 has a disadvantage that, in order to detect a cable length, a control cable is required to be additionally arranged in addition to the cable for transmitting a drive signal for driving the CCD and the cable for transmitting the image signal read out from the CCD to the video processor section and, thus, the arrangement is correspondingly complicated in structure. Particularly, in a case of a video end scope, since it is necessary or required to reduce a diameter of an inserting section, it is extremely difficult to additionally arrange the cable.
Moreover, the television camera apparatus disclosed in Japanese Patent Laid-Open No. SHO 61-187470 is influenced upon the reset signal due to amplitude of the image signal since the sampling pulse is prepared or generated by the reset signal including an image signal duration which is sent from the CCD. Thus, it is difficult to prepare steady and accurate or exact sampling pulse. Furthermore, in a case where delay equal to or more than one or single picture element occurs in the image signal, following is performed with respect to the sampling pulse every one picture element. However, it is difficult to exactly generate a sampling pulse every equal to or more than two picture elements as is in color demodulation of a single-plate color tip camera having a mosaic color filter.
In view of the above, a television camera apparatus is disclosed in Japanese Patent Laid-Open No. HEI 1-132280 (132280/1989) in which a reset signal only in an invalid image area or region of an image signal is extracted to regenerate a sampling pulse.
A conventional example will hereunder be described with reference to the accompanying drawings.
As shown in FIG. 35, a standard signal generator (hereinafter referred to "SSG1") 81 generates CCD drive pulses (.phi.R, .phi.H1, .phi.H2) which are outputted to a CCD driver 84 for driving a solid-state image pickup element, for example, a CCD 83, from an output from a quartz generator (hereinafter referred to as "CXO") 82. As shown in FIG. 36, each of the CCD drive pulses is divided into an image signal section and a cable-length correcting pulse section during one cycle of a horizontal synchronous signal. At the image signal section, the CCD 83 is driven by CCD drive pulses of .phi.R, .phi.H and .phi.V. At the cable correcting pulse section, the CCD 83 is driven only by .phi.R of duty of 50%. In the image pickup signal from the CCD 83 driven in this manner, the cable-length correcting pulse section is extracted by a mask signal (FIG. 37) from an SSG2 (86) at a mask circuit 85. The image pickup signal from the CCD 83 is formed into a digital signal by a limiter amplifier 87. Further, the image pickup signal from the CCD 83 is compared in phase with an output from a voltage control oscillator (hereinafter referred to as "VCXO") 89 by a phase comparing circuit 88. The VCXO 89 is controlled by an output from the phase comparing circuit 88. Thus, a phase of the output from the VCXO 89 is conformed to a phase of waveform of the cable-length correcting pulse section. A PLL is arranged in this manner, the CDS clock is generated at a CDS clock generator 90 on the basis of an output from the VCXO 89 which is synchronized with the waveform of the cable-length correcting pulse section, and a CDS 91 performs correlation double sampling with respect to the image pickup signal by the CDS clock, to thereby obtain an image signal of a base band. Further, the SSG2 (86) generates a timing pulse for an image signal on the basis of an output from the VCXO 89 and H and V reset signals from the SSG1 81. An image processing circuit 92 processes in signal the output from the CDS 91 and performs outputting as a normal or usual image signal (FIG. 38).
In this manner, conventionally, since signal processing is performed on the basis of the waveform at the cable-length correcting pulse section which is superimposed upon the output from the CCD 83, a propagation delay-time error due to the cable length can be corrected to perform signal processing.
However, also in Japanese Patent Laid-Open No. HEI 1-132280, measures are not taken with respect to delay equal to or more than two picture elements due to the cable.
Moreover, the above-described prior art has the following disadvantages. That is, since the cable-length correcting pulse is superimposed into the form of burst every horizontal synchronization, time is taken from a condition in which lock of a PLL is off upon turning-ON of a power source and so on to a condition where the PLL is locked, so that the image signal is disturbed.